1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to wireless communication technology, and more particularly, to efficiently transmitting and receiving uncompressed audio/video data by using unequal error protection during high-frequency wireless communication, as well as a transmission frame structure to which unequal error protection is applied.
2. Description of the Related Art
Wireless networks are extensively used in the industry, and there exists an increased demand for large-capacity multimedia data transmission. Consequently, much research is being conducted with regard to efficient transmission methods in wireless network environments. Particularly, demand is growing for high-quality video data (e.g., digital versatile disk (DVD)-grade or high definition television (HDTV)-grade video data) transmissions between various home devices in a wireless manner.
The Institute of Electrical and Electronics Engineers (IEEE) 802.15.3c task group is in the process of establishing a technical standard regarding large-capacity data transmission in wireless home networks. This standard, referred to as Millimeter Wave (mm Wave), utilizes radio waves having a millimeter wavelength (i.e., radio waves having a frequency of 30 GHz to 300 GHz) for large-capacity data transmissions. This range of frequency has been used in related art as unlicensed bands for limited applications (e.g., for communication operators, radio astronomy, and vehicular collision avoidance).
FIG. 1 shows the comparison between the frequency band of the IEEE 802.11 series standards and that of mm Wave. It is clear from the drawing that the IEEE 802.11b standard or the IEEE 802.11g standard has a carrier wave frequency of 2.4 GHz and a channel bandwidth of about 20 MHz. In addition, the IEEE 802.11a standard or the IEEE 802.11n standard has a carrier wave frequency of 5 GHz and a channel bandwidth of about 20 MHz. In contrast, mm Wave has a carrier wave frequency of 60 GHz and a channel bandwidth of about 0.5-2.5 GHz. As such, compared with conventional IEEE 802.11 series standards, mm Wave has much higher carrier wave frequency and a larger bandwidth. Such use of high-frequency signals having a millimeter wavelengths (i.e. millimeter waves) ensures a very high transmission rate (measured in Gbps). Since antennas having a size of 1.5 mm or less are used, a single chip incorporating the antennas can be realized. Furthermore, a very high attenuation ratio in the air reduces the interference between devices.
Presently, various research is being conducted to see how well uncompressed audio or video (AV) data can be transmitted between wireless devices using millimeter waves. When the compressed AV data undergoes motion compensation, discrete cosine transform (DCT) conversion, quantization, and variable-length coding so as to remove parts to which the human visual and auditory senses are less sensitive, information is lost. In contrast, uncompressed AV data retains digital values indicating pixel components (e.g., red (R), green (G), blue (B) components).
As such, bits included in compressed AV data have the same degree of significance while those included in uncompressed AV data have different degrees of significance. In the case of the eight-bit image shown in FIG. 2, for example, a pixel component is expressed by eight bits. A bit indicating the highest order (bit at the topmost level) is the most significant bit (MSB), and a bit indicating the lowest order (bit at the bottommost level) is the least significant bit (LSB). Namely, each bit of one-byte data, which consists of eight bits, has different degrees of significance in restoring video or audio signals. When an error has occurred in a bit having higher significance, the error is more likely to be detected than in the case of a bit having lower significance. This means that bit data having higher significance must be protected against errors during wireless transmission with higher certainty than that of bit data having lower significance. However, related art transmission modes based on the IEEE 802.11 series standards employ error protection and retransmission modes using the same coding ratio for all bits to be transmitted.
FIG. 3 shows the structure of a physical (PHY) Protocol Data Unit (PPDU) 30 of the IEEE 802.11a standard. The PPDU 30 includes a preamble, a signal field, and a data field. The preamble consists of signals for PHY layer synchronization and channel estimation, particularly a plurality of short training signals and long training signals. The signal field includes a RATE field indicating the transmission rate and a LENGTH field indicating the length of the PPDU. The signal field also includes a reserved bit, a parity bit, and a tail bit. The signal field is generally coded by a symbol. The data field consists of a physical layer service data unit (PSDU), a tail bit, and a pad bit. The PSDU contains data to be transmitted.
The data recorded on the PSDU is composed of codes which have been encoded by a convolution encoder or Reed-Solomon (RS) encoder. The data has the same degree of significance and is coded under the same error protection. Consequently, each part of the data has the same error protection capability. When the reception side finds an error and solicits retransmission from the transmission side (e.g., via an acknowledgment (ACK)), the transmission side retransmits all of the corresponding data. Such a related art method has a problem in that, apart from normal data transmission, the significance of data to be transmitted varies. This degrades the transmission condition of the channel.